1. Field of Invention
The invention relates to a safety device for an electric control or regulating system for a gearshift mechanism which contains at least one electromagnetic control element.
2. Description of the Prior Art
German Patent 34 05 289, which corresponds to U.S. Pat. No. 4,661,772, issued to the inventor herein, discloses an electric measuring and testing circuit for a control system of a gearshift mechanism. A control system for a gearshift mechanism is disclosed in German Patent 35 06 849.
Electrically actuated magnets, so-called gearshift magnets, are provided to change the gears in gear shifting mechanisms of a known type. Moreover, a mechanical shifter has heretofore been provided for each gear, and thus also for each shift magnet. If a gear magnet was supplied with current, the mechanical shifter for this gear magnet mechanically changed the mechanical shifter of the previously engaged shift magnet such that only that gear was engaged, the shift magnet of which was last energized. The individual gears therefore have always been changed "mechanically" by the shifter. Each gear had a shifter. The shifter of the new gear automatically unlocked the shifter of the old gear and pushed it aside and locked in the newly engaged gear.
In this way it was assured that in all cases only the shift clutch of the last gear engaged was actuated, but never a plurality of clutches of a plurality of gears simultaneously.
In another known type of gearshift mechanism, when shifting from one gear to another, the clutches for the two gears are engaged "overlappingly", such that the clutches of the two gears are actuated simultaneously during a shift period. Both clutches slip simultaneously and thus both take over part of the job of synchronization for the gearshift. At the same time, the engaging pressure of the friction surfaces in the two clutches must be so controlled that, after a certain slippage period, during which both clutches are slipping, the clutch of the previous gear is fully opened and the clutch of the newly engaged gear is completely closed, that is, one clutch is opened so far, that it no longer slips, and the other clutch is closed with such a strong pressure that it no longer slips. At the same time, it is necessary that the clutches do slip simultaneously during a shift period, yet never must both be closed simultaneously so fully that they no longer slip, but are closed so as to block without slippage.
For this kind of "overlapping" gear change with simultaneously slipping clutches for several gears, the above-mentioned mechanical shifters can no longer be used, since they would prevent this kind of overlapping gear change. The mechanical shifters, however, have the advantage that, in the event of a power failure, the last-engaged gear continues to be engaged, and that, in the event of an electrical short circuit, a plurality of gears will not become engaged simultaneously, which would lead to a breakdown of the gear shifting mechanism. The problems therefore faced by the newly developed transmissions with "overlapping" engagement are as follows:
1. How can the last-engaged gear be kept engaged in the event of an electrical power failure, and PA1 2. How can it be assured, in the case of an electrical short circuit or other defect, that two or more gears will not become engaged simultaneously and thus cause transmission damage?
This means that an "overlapping slippage" of the clutches would be desired in the new gear shifting mechanism, but not the complete and simultaneous closing of the clutches of two or more gears. Also, in the case of a defect, such as an electrical voltage drop or an electrical short circuit, the disadvantages described above should be avoided. The mechanical shifters of the state of the art do permit an "overlapping slippage" of the clutches of successively engaged gears, but only insofar as production tolerances allow it and as a result of the flow time of the actuating oil. However, they do not permit a controlled overlapping slippage of the clutches for a specific slippage period. Pursuant to the invention, the duration of the gear changing process and the period of common slippage of the clutches can be made dependent on the torque that is to be transferred.